Now, with the Dow at a record, the Maestro declares stocks to be
"undervalued," an assertion that might be open to reasonable
debate. It does, however, reflect the increasingly ebullient
sentiment becoming more pervasive not only among the financial
elite, such as the former Fed chairman, but also celebrities far
removed from the markets.

And individual investors are getting exuberant too:

Other signs of frothy sentiment also have been bubbling up,
notably a jump in bullishness among investment advisory services
polled by Investors Intelligence. Bulls increased sharply to
50.0% last week from 44.2%, while outright bears fell to 18.8%
from 21.1%, their largest weekly drop in 10 months. Advisors
looking for a correction also dwindled to 31.2% from 34.7%.
Moreover, the spread between bulls and bears surged to 31.2% from
23.1% in just a week and put it in "the dangerous territory
around 30%," Investors Intelligence commented. A wide spread a
year ago preceded a market retreat, the service noted.

Other signs that might make you kind of nervous, per the piece.
Dow Transports are getting massively extended, and the number of
NYSE new highs is actually dwindling, suggesting that the market
gains are very concentrated.